1. Field of the Invention
This invention pertains generally to video coding, and more particularly to controlling inter-prediction in a B-picture during video coding.
2. Description of Related Art
Efficient video storage and communication requires coding mechanisms for reducing spatial and temporal redundancies. Ongoing efforts are directed at increasing the efficiencies of these enCOder/DECoders (codecs) which respectively compress and decompress video data streams. The purpose of codecs is to reduce the size of digital video frames in order to speed up transmission and save storage space. Video coding advances have collectively contributed to the high levels of coding efficiency provided by state-of-the-art codecs. The latest of these developing coding standards is referred to as High Efficiency Video Coding (HEVC), from the Joint Collaborative Team on Video Coding (JCT-VC), which is a joint effort of the MPEG and VCEG standardization committees.
Three different types of frames are encoded, I, P and B frames. Intra coded (I) frames are coded based on spatial redundancy only, without benefit of dependence on surrounding frames. Predicted coded (P) frames are coded using prediction from prior encoded I or P frame(s). Bi-directional coded (B) frames are coded with bi-directional (forward and backward) prediction information, yet are never used for P frame prediction. The benefit of providing forward encoding is the ability to match a background area that was occluded in the previous frame. Bi-directional prediction allows for decreased noise by averaging both forward and backward prediction. It will be noted that coding B frames is more complex since frames are decoded out of order with respect to the order in which they are captured or are to be displayed.
The type of encoding is determined within the encoder for each frame, and the coding type is communicated to the decoder so that it can properly decode the frames. Modern encoders are configured within a B-frame for performing a single prediction of either direction, or a bi-directional prediction taking one motion vector from each list, and does not always provide optimum prediction.
Accordingly, the present invention provides enhanced prediction and overcomes shortcomings of previous approaches.